Method of making spool valves

ABSTRACT

A method of making a spool valve includes forming perforations in the core and sleeve members of the valve in a single machine operation. The perforations are formed offset from and parallel to a plane which includes the axis of the core and sleeve members. The perforations may take a wide variety of shapes including round, rectangular or peripheral channels. The valve becomes functional by rotating or longitudinally adjusting the relative positions of the core and sleeve members to selectively align or block the perforations of the core member with respect to the sleeve member.

United States Patent 1191 Tobias Sept. 10, 1974 METHOD OF MAKING SPOOLVALVES 3,052,013 9/1962 Kane 29/157.1 R [76] Inventor: John D. Tobias,233 E. Bloomfield, gi s l 29/423 y er 29/526 Royal Oak, Mlch- 480733,685,135 8/1972 Letters 29/445 [22] Filed: Oct. 24, 1972 PrimaryExaminer-Charles W. Lanham [21] Appl' 300166 Assistant ExaminerD. C.Crane Related US. Application Data Attorney, Agent, or Firm-Hauke,Gifford, Patalidis & [60] Continuation-impart of Ser. Nos. 282,964, Aug.23, Dumont 1972, abandoned. Continuation-in-part of Ser. No. 230,845.March 1, 1972, abandoned. Division of Ser. N0. 97.140. Dec. 11. 1970.Pat. N0. 3.700,004. [57] ABSTRACT A method of making a spool valveincludes forming Cl 137/625.23 perforations in the core and sleevemembers of the [51] Int. Cl 823p 13/00 valve in a single machineoperation. The perforations Field of ch 29/l57-1 R, 32, 4 are formedoffset from and parallel to a plane which 62521, 625-2 includes the axisof the core and sleeve members. The

perforations may take a wide variety of shapes includ- [56] ReferencesCited ing round, rectangular or peripheral channels. The UNITED STATESPATENTS valve becomes functional by rotating or longitudinally 686 31111/1901 Leaycraft 29/526 adjusting the relative Positions of the coreand Sleeve 9721292 10/1910 Thomas 291432 members to Selectively align orblock the perforations 1,154,746 9/1915 Champ 137/625.23 of the coremember with respect to the sleeve mem- 2,328,606 8/1943 Boldt 137/625.23ber. 2,595,695 5/1952 Packer et al 29/445 17 Claims, 29 Drawing FiguresPAIENIEDSEPI 0 14 a; 838 ees sum 1 OF 4 Y I PAIENTED SEPI 0:914

sumeom 1 METHOD OF MAKING SPOOL VALVES RELATIONSHIP TO OTHER PATENTAPPLICATIONS This application is a division and continuation-in-part ofcopending US. Pat. application Ser. No. 97,140 filed Dec. 11, 1970,entitled Valve Structure and Boost Control System, now US. Pat. No.3,700,004. This application is also a continuation-in-part of copendingapplication entitled Valve Construction, Ser. No. 230,845, filed Mar. 1,1972 and of copending application entitled Methods of Making SpoolValves, Ser. No. 282,964 filed Aug. 23, 1972, both now abandoned.

BACKGROUND OF THE INVENTION I. Field of the Invention This inventionrelates to methods of manufacturing spool valves for fluid controlsystems. Spool valves of the type dealt with herein consist essentiallyof a generally cylindrical sleeve member, a generally cylindrical coremember rotatably mounted in said sleeve, perforations in the sleevewhichserve as fluid inlet and output ports, and perforations in the corewhich register for fluid flow with selected sleeve perforations uponrotation of the core relative to the sleeve.

II. Description of the Prior Art Spool valves of many types withnumerous porting variations are used in all types of fluid power andfluid control systems, generally requiring specialized and difficultmanufacturing processes. With requirements for more complex fluidsystems, valves have tended to become more complex, thus causingincreases in costs and problems of reliability. Simpler valvefabrications methods are highly to be desired.

SUMMARY OF THE INVENTION In the manufacture of a spool valve the methodof the invention is carried out with thecore and sleeve of the valvebeing fixed against rotational or longitudinal movement relative to eachother. The valve, when so fixed is in the manufacturing position. Whilethe valve is in the manufacturing position a single machine operation isperformed on both core and sleeve. For example, the valve is held in adrill press and a hole is drilled through one wall of the sleeve andpartway into the core. The perforations, because they are formed in asingle machine operation, have congruent boundaries at the interfacebetween; core and sleeve. It is an additional feature of the inventionthat the perforations made in the manufacturing position are offset fromand parallel to a plane which includes the longitudinal axis of the coreand sleeve.

The perforations may be circular, rectangular, channel shaped, or thelike, and may be made by drilling, grinding, electrical dischargemachining, or the like. A perforation made by a single machine operationmay extend, for example, through one side of the sleeve and entirelythrough the core or, for example, may extend entirely through the sleeveand entirely through the core. Further, there may be groups of suchperforations each group spaced .longitudinally from another, each madein a single machine operation, and one coacting with another when thevalve is in a functional position.

The valve is changed from its manufacturing position to its functionalposition (a) by revolving the core to effect a change in the radialposition of the core relative to the sleeve, (b) by moving the corelongitudinally relative to the sleeve, (0) by reversing the coreend-forend relative to the core, or (d) by a combination of suchmovements.

Similarly, perforations of the type described may be made in the sleeveand core in a first manufacturing position followed by movement of thecore and sleeve, longitudinally or radially, relative to each other to asecond manufacturing position. Another set of perforations can then bemade by a single machine operation in said second manufacturingposition. 1

DESCRIPTION OF THE DRAWINGS For a more complete understanding of theinvention, reference may be had to the accompanying drawingsillustrating preferred embodiments thereof in which like referencecharacters refer to like parts throughout the several views, and inwhich:

FIG. 1 is an exploded perspective view of a spool valve assembly made bymethods embodying the invention;

FIG. 2 is a diagrammatic cross-sectional view of a spool valve assemblyand tool following the making of a port-forming perforation,

FIG. 3 is a diagrammatic cross-sectional view of the assembly of FIG. 2with the core rotated to its neutral operative position,

FIG. 4 is a diagrammatic cross-sectional view of the spool valveassembly and tool following the making of a second, and alternative,port-forming perforation,

FIG. 5 is a diagrammatic cross-sectional view of the assembly of FIG. 4with the core rotated 180 to its neutral operative position,

FIG. 6 is an exploded perspective view of a third spool valve made by amethod embodying the invention,

FIG. 7 is a cross-sectional view taken in the plane of lines A-B and C-Dof FIG. 6 in the manufacturing position,

FIG. 8 is similar to FIG. 7 but with the core rotated 180 relative tothe sleeve,

FIG. 9 is similar to FIG. 7 following rotation of the core memberrelative to the sleeve member to a second and operational position,

FIG. 10 is similar to FIG. 7 following rotation of the core memberrelative to the sleeve member to a third and operational position,

FIG. 11 is a cross-sectional view of a fourth spool valve modificationin its manufacturing position and including two peripheral channels,

FIG. 12 is a cross-sectional view of the spool valve of FIG. 11following rotation of the core member relative to the sleeve member to asecond and operational position,

FIG. 13 is a cross-sectional view of the spool valve of FIG. 11following rotation of the core member relative to the sleeve member to athird and operational position,

FIG. 14 is a perspective view of a fifth valve and a machine tool forforming a peripheral channel, said valve being in a first manufacturingposition;

' FIG. 15 is aperspective view of thevalve of FIG. 14 wherein the corehas been rotated 180 relative to the sleeve to a second manufacturingposition,

FIG. 16 is an exploded perspective view of the valve of FIGS. 14 and 15with additional perforations for a complete functional valve,

FIGS. 17A, 17B, 17C, and 17D are cross-sectional views taken along theline EF of FIG. 14 and showing, respectively, the first manufacturingposition, the second manufacturing position, a first operationalposition, and a second operational position,

FIG. 18A, 18B, 18C, and 18D are cross-sectional views taken along theline G-l-I of FIG. 16 and showing, respectively, the first manufacturingposition, the second manufacturing position, a first operationalposition and a second operational position,

FIG. 19 is a perspective view of a sixth spool valve in a firstmanufacturing position;

FIG. 20 is a perspective view of the valve of FIG. 19 in a secondmanufacturing position wherein the core of FIG. 19 has been movedlongitudinally relative to the sleeve;

FIGS. 21A and 21B are cross-sectional views taken along the line J-K ofFIG. 20 and showing, respectively, the first manufacturing position andthe second manufacturing position of the valve of FIG. 20, an

FIG. 22 is a cross-sectional view taken along the line L-M of FIG. 20and shows the second manufacturing position of the valve of FIG. 20.

DESCRIPTION OF THE PREFERRED METHODS FIG. 1 illustrates in exploded viewa valve assembly 10 as comprising a cylindrical sleeve member 12 havinga longitudinal bore 14 extending therethrough and adapted to closelyenclose a cylindrical hollow core member 16.

The sleeve member 12 is perforated on transverse axes A and B, formingports 18, 20, 22 and 24 as shown, while the core member 16 is perforatedon axes A and B, forming ports 26, 28, 30 and 32. It will be seen thatthe perforation axes A and B are longitudinally spaced and laterallyoffset on opposite sides and parallel to a plane P which contains thelongitudinal axis X of the sleeve member 12, which axis is of coursecommon to the longitudinal axis of the core member 16. The perforationaxes A and B are likewise longitudinally spaced and laterally offset onopposite sides and parallel to the plane P, but, as oriented in FIG. 1,the core member 16 has been rotated 180 from its initial formed positionwithin the sleeve member 12 so that the axes A and B are respectively onopposite sides of the plane from the axes A and B.

When manufactured as shown it will be seen that the core member 16 maybe reversed end-for-end relative to the sleeve member 12 without problemor difference in port relationships, making assembly no problem as faras correctly orienting the components.

Also, it will be noted in this specific embodiment that the ports areall preferably tangentially adjacent the plane P such that, in theorientation shown, the sleeve ports will be closed off from the coreports, providing for the desired operation of this valve as will bedescribed hereinafter.

If desired, the sides of the ports, or some of them, may extend throughthe plane P to provide an overlap in which sleeve and core ports will beopen to each other a prescribeddegree, or alternatively, some or all theports may be slightly spaced from the plane P to provide for aprescribed degree of rotation of the core 16 in the sleeve 12 to eitherside of the 180 initial rotated position during which the ports willremain closed.

FIG. 2 shows, cross-sectionally, a sleeve member enclosing a core member16a and a tool 34a adapted to form in a single operation, a port 18a inthe sleeve member 12a and ports 28a and 26a in the core member 16a, allon the common perforation axis A which is laterally offset from theplane P which contains the longitudinal axis X.

FIG. 3 shows the sleeve member 120 and core memher relatively rotatedsuch that the core ports 26a and 28a now lie on the perforation axis Aoffset on the opposite side of the plane P from the axis A.

In use, rotation of the core member 160 clockwise from the position ofFIG. 3 will variably open the port 26a to the port 18a, while the port280 is unused.

FIG. 4 shows a sleeve member 12b enclosing a core member 16b and a tool34b adapted to form in a single operation, ports 18b and 20b in thesleeve member 12b, and ports 28b and 26b in the core member 16b, all onthe common perforation axis A which is laterally offset from the plane Pwhich contains the longitudinal axis X FIG. 5 shows the sleeve member12b and core mem- I ber 16b relatively rotated 180 so that the coreports 26b and 28b now lie on the perforation axis A offset on theopposite side of the plane P from the axis A. In use, rotation of thecore member 16b clockwise will variably open the port 26b to the port18b, and rotation counterclockwise will variably open the port 28b tothe port 20b.

It will be seen that certain ports of FIG. 1 may be thus formed in anextremely simple fashion. The sleeve 12 and core 16 are fixed relativeto each other in a manufacturing position (the core being rotated 180relative to its position in FIG. 1). A single drilling operationproduces the holes 18, 28, 26, and 20 and a second, and again a singledrilling, operation produces holes 22, 32, 30, and 24. Therefore, on a360 rotation from the position shown, in the direction indicated by thearrow, (FIG. 1), the valve portion will be in accord with the followingschedule:

1. Ports 28 and 30 open to ports 20 and 22, then close; 2. Dwell period;3. Ports 28 and 30 open to ports 18 and 24, and simultaneously ports 26and 32 open to ports 20 and 22, then all close simultaneously;

4. Dwell period;

5. Ports 26 and 32 open to ports 18 and 24, then close, following which,on continued rotation, step (1) repeats with no dwell.

FIG. 1 also shows an arcuately extending or peripheral channel port 36in the sleeve member 12, and a port 38 provided in the side of the coremember 16 on the plane P, these ports being longitudinally spaced fromand preferably intermediate the previously described ports which areoffset from the plane P. This construction enables one to connect afluid source to the port 36 to introduce fluid into the center of thecore member 16 through the port 38, and the other sleeve ports 18, 20,22, and 24 may be connected as desired into a fluid user system so thatrotation of the core will selectively variably alternatively openvarious sleeve ports to fluid inside the core. Such a valve assembly hasinnumerable uses in fluid control systems. It will be apparent thatports 36 and 38 are not made in a single machine operation and theirmethod of manufacture is not a part of the invention claimed herein.

Alternatively, the ports 36 and 38 could be eliminated and fluid couldbe introduced into the core member 16 axially, and rotation of the core16 would selectively variably alternatively open the sleeve ports tothis fluid.

It is also noted that the core member 16 may be shifted axially withinthe sleeve member 12 to longitudinally offset the core and sleeve ports,such that on rotation the ports will not open until the core is shiftedback. Alternatively, a second set of sleeve ports could be provided,with the core member 16 shifting as desired, to permit alternativeregistry of its ports with either set of sleeveports.

Further, additional ports may be similarly formed to increase the numberof fluid connections, and ports may be offset relative to other planescontaining the axis A but rotated relative to the plane P of FIG. 1.

FIG. 6 illustrates in exploded view another type of spool valve whichutilizes the method of the invention in its manufacture. The valve isindicated generally by reference numeral 31, and comprises a core member33 which can be rotatably mounted in a longitudinal bore 35 of a sleevemember 37.

The sleeve member 37 is perforated at 39 on an axis A-B transverse to anaxis X of the core and sleeve members and offset from a plane P whichincludes the axis X. The perforation 39; in a first position, amanufacturing position, of the core 33 relative to the sleeve 37;registers with perforation 40 in the core member 33, the perforations39, 40 forming a peripheral channel with congruent boundaries at therespective interface of the channel in the core member 33 and the sleevemember 37 (see FIG. 7). The peripheral channel can be made by a singleshaping or grinding operation such as is described more fully inconnection with FIG. 14.

The sleeve member 37 is also perforated at 42, 44 on an axis CDtransverse to axis X. The perforation 42, 44 in a first position of thecore 33 relative to the sleeve 37, registers with a core perforation 46forming a cylindrical hole with congruent boundaries at the respectiveinterfacesof the hole in core member 33 and sleeve member 37 (see FIG.7). The holes 42 and 44 in the sleeve 37 and the hole 46 in the core 33are made by a single drilling operation, as by drill 34a, see (FIG. 2).An intermediate perforation 48 is made in the sleeve only in a separatemachine operation.

Referring to FIGS. 7-10 inclusive, four positions of the core 33 of FIG.6 relative to the sleeve 37 are shown. FIG. 7 illustrates the first, ormanufacturing, position. It can be seen in FIG. 7 that a transverseperipheral channel can be made through the core 33 and sleeve 37 toform, by a single machine operation, the core perforation 40 and thesleeve perforation 39. Similarly, it can be seen that a transversecylindrical or other shaped hole can be made by a single machineoperation to form core perforation 46 and sleeve perforations 42, 44. Ahole 48 in sleeve 37 is made in a separate machine operation.

FIG. 8 is the same as FIG. 7 except that the core 33 has been rotated180 relative to the sleeve to a dwell, or off position of the valve.

FIG. 9 is the same as FIG. 8 except that the core 35 has been rotatedclockwise to an operational position wherein thesleeve perforations 39and 44 both register ation and the channels 52 and 56 are made in asingle machine operation. Intermediate perforations 58 and 60 are madein the sleeve only by a separate machine operation. FIGS. 12 and 13 showrespectively operational positions of the valve of FIG. 11 in the samemanner as shown in FIGS. 9 and 10 for the valve of FIG. 7. v

FIGS. 14 through 18D illustrate an embodiment o the invention in whichthere are two manufacturing positions of the core relative to the sleeveand wherein the two manufacturing positions are displaced radially fromeach other. FIG. 14 shows a spool valve wherein theposition of a core 62has been fixed relative to a sleeve 64 in the first manufacturingposition. In said first manufacturing position a shaping tool 66, in asingle operation, is used to fomi a peripheral channel 68 in sleeve 64and a peripheral channel 70 in core 62. Channels 68 and 70 havecongruent boundaries at their interface between core and sleeve and liegenerally in a plane parallel to and offset from plane P which includesthe axis X of the valve.

FIG. 15 shows the valve of FIG. 14 fixed in its second manufacturingposition wherein the core 62 of FIG. 14 has been rotated 180 relative tosleeve64. In the latter position a hole 72, 74, and 76 is drilledthrough sleeve 64 and core 62 in a single drilling operation with adrill 77. The latter hole is also in a plane offset from plane P and,further, is spaced longitudinally from peripheral channels 68 and 70.

FIG. 16 shows, in exploded view, the valve of FIGS. 14 and 15 withadditional functional features such as an axial extending'hole 78 incore 62, a hole 80 providing fluid connection between peripheral channel70 and the axial hole 78, a hole 82 in sleeve 64, and a secondperipheral channel 84 in core 62. In the specific embodiment illustratedperforations 78, 80, 82, and 84 are each formed in a separate machineoperation and not by the method of the invention. A handle (not shown)can be secured to stem 85 for the purposes of rotating the core 62relative to the sleeve 64.

FIGS. 17A, 17B, 17C, and 17D illustratefour positions of the core 62relative to the sleeve 64 with the view being the cross-section of thevalve taken through peripheral channels 68 and 70.

FIGS. 18A, 18B, 18C, and 18D illustrate, respectively, the samepositions of the core and sleeve except that the view is of across-section of the valve taken through peripheral channel 84 and holes72, 74, 76, and 82. Axial hole 78 provides fluid communication betweenthe group of perforations shown in FIG. 17A, etc. and the group ofperforations shown in FIG. 18A, etc.

Thus FIGS. 17A and 18A illustrate the respective sections in the firstmanufacturing position (with all manufacturing completed) and FIGS. 17Band 18B illustrate the respective sections in the second manufacturingposition. FIGS. 17C and 18C illustrate a third and operational positionin which a first fluid stream enters channel 68, passesthrough channel70, hole 80, axial hole 78, hole 74, and discharges through sleeve port72 while a second fluid stream enters sleeve port 76, passes throughperipheral channel 84, and discharges through sleeve port 82. FIGS. 17Dand 18D illustrate a fourth and operational position in which a secondfluid stream enters channel 68, passes through channel 70, hole 80,axial hole 78, hole 74, and discharges through sleeve port 76 while asecond fluid stream sleeve port 72, passes through peripheral channel84, and discharges through sleeve port 82.

FIGS. 19 through 22 illustrate an embodiment of the invention whereinthere are two manufacturing positions spaced longitudinally from eachother.

FIG. 19 illustrates a first manufacturing position in which the positionof the core 86 is secured against rotational or longitudinal movementrelative to sleeve 88 while, in a single machine operation such as byshaping tool 66 (FIG. 14), peripheral channels 90 and 92 are made incore 86 and sleeve 88 respectively.

FIG. 20 illustrates a second manufacturing position wherein the core 86of FIG. 19 has been moved longitudinally to the left (as shown). In thelatter position hole 94, 96, and 98 is drilled, in a single machineoperation with drill 77, completely through the core 86 and the sleeve88. Auxiliary perforations such as axial hole 100, (FIG. 21A) hole 102joining channel 92 and axial hole 100, (FIG. 21B) and hole 104; (FIG.22) are formed in separate machine operations.

FIG. 21A illustrates the position of core 86 relative to sleeve 88 inthe first manufacturing position of the valve of FIG. 19 by across-sectional view taken through the channels 90 and 92. FIGS. 21B and22 show the position of core 86 relative to sleeve 88 in the secondmanufacturing position by, respectively, crosssectional views takenthrough section J-K and section L-M of FIG. 20. Axial hole 100 providesfluid connection between the group of perforations shown in FIG. 21B andthe group of perforations shown in FIG. 22.

The operational positions of the valve shown in FIGS. 19 through 22 isthe same as that already shown in FIGS. 17C, 17D, 18C, and 18D.

The various perforations formed by the method of the invention in thecore and sleeve members of spool valves may be formed in a number ofdifferent positions other than those illustrated. In general, at leastone perforation in the core is disposed to be aligned with at least oneperforation in the sleeve with such perforations being parallel to andoffset from a plane which includes the axis of the core and sleeve.

Various shaped perforations may be formed by the methods of the presentinvention. Rectangular or square ports may sometimes be desirable wheresurging of the fluid is desirable. Round ports, on the other hand,minimizes surging.

The materials of which the core and sleeve members are formed mayinclude metal, plastic, synthetic materials or any other suitablematerial dependent upon the particular application involved and theproperties of the fluid passing through the valve.

When metal is the material involved, methods involving EDM and ECMmachining are especially suitable. Such a method is desirable because ofits adaptability to the wide variations generally necessary to satisfyvalve porting requirement. EDM and ECM machining methods are well knownto those skilled in the art. Such methods involve placing an electrodeand the part to be machined in a suitable conductive solution. A voltageis applied across the electrode, which may be considered an anode, andthe part to be machined, which may be considered a cathode. Theelectrode is shaped to the shape of the portion of the part to be erodedto provide the desired opening or openings in the core and spool.

One preferred method in practicing the present invention involves usingepoxy or other suitable adhesive to hold the sleeve and core blankstogether temporarily during a machine operation in a manufacturingportion. After machining the members by EDM or other machine methods,the members may be immersed in hot water, for example, to melt the epoxyor other adhesive; thus permitting the parts to be separated, cleaned,lubricated, and then assembled in appropriate housings (not shown) foroperational use as hereinbefore described. Such a method may beperformed relatively inexpensively with high precision of the portsformed congruently in the members.

In the present methods discussed, it is apparent that a plurality ofgroups of perforations may be simultaneously formed in the core andsleeve. For example, a grinding tool may make a peripheral channel incore and sleeve while a drill is making a hole through core and sleevein the same manufacturing position.

The type of method used to form the various perforations in the sleeveand core depends to some extent upon the quantity of valves to beformed, the material of which the parts forming the valves are to bemade, and other factors. For example, the setup for an EDM method may berelatively expensive for simple shapes involving only a small number ofparts, while being justified when more complex perforation shapes areinvolved.

Depending upon the design and quantities involved, in addition to EDM,the methods involved may involve drilling, broaching, jig boring,grinding or milling. The final precision may involve additional sizingwith suitable lapping or honing operations as may be required.

It will be apparent to one skilled in the art to which the inventionpertains that various changes and modifications may be made thereinwithout departing from the spirit of the invention or the scope of theappended claims.

What I claim is:

1. A method of making a spool valve structure having a cylindrical coremember rotatably enclosed in a sleeve member, said method comprising thestep of forming in a single machine operation a first perforationentirely through both of said members on a transverse axis parallel toand offset to one side of a plane containing the longitudinal axes ofsaid 2. The method according to claim 1 wherein said members areretained against movement relative to each other during said formingoperation.

3. The method according to claim 2 and including the step of forming asecond perforation as therein defined, said two perforations beingspaced radially from each other.

4. The method according to claim 2 and including the step of forming asecond perforation as therein defined, said two perforations beingspaced longitudinally from each other.

5. The method according to claim 3 and including forming said first andsecond perforation on axes offset from opposite sides of said plane.

6. The method according to claim 4 and including forming said first andsecond perforation on axes offset from opposite sides of said plane.

7. The method according to claim 4 and including the step of forming anaxially extending hole in said core member to effect fluid connectionbetween said first and second perforations.

8. The method according to claim 2 wherein said perforation is in theform of a peripheral channel with congruent boundaries at the interfaceof said core and sleeve members.

9. The method according to claim 8 wherein a second peripheral channelis formed in said core.

10. The method according to claim 2 wherein said perforation is agenerally cylindrical hole with congruent boundaries at the interface ofsaid core and sleeve members.

11. The method according to claim 4 wherein said first perforation is aperipheral channel and said second perforation is a cylindrical hole.

12. The method according to claim 4 wherein both said perforations areperipheral channels.

13. The method according to claim 1 and including forming a secondperforation in said sleeve member intermediate said two ports.

14. The method according to claim 2 in which said forming operation iselectrical discharge machining.

15. The method according to claim 2 wherein the step of retaining saidcore and sleeve members against movement comprises applying an adhesivematerial to said members prior to said forming operation and removingsaid adhesive material subsequent to said forming operation.

16. The method according to claim 14 and including using a meltableepoxy material to retain said sleeve and core member against movement.

17. The method according to claim 15 and including the steps of usingelectrical discharge machining and then melting said epoxy material topermit said core and sleeve members to be separated from each otherfollowing the perforation forming step.

UfiITED STATES PATENT OFFICE CERTIFICATE, OF CORRECTION- Patent No.3,833,988 Dated 9-10-74' Inventor(s) h n Tobias It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Col. 3, line 23, "an" should be --ana--.'

I Col. 8', l ihe 56, after "said" insert -members--.

Signed and sealed this 19th dey of November 1974.

(SEAL) Attest:

McCOY M. GIBSONJR. CQMARSHALL DANN- Attesting Officer Commissioner ofPatents USCOMM-DC 6087 6 P69 FORM PO-105O (10-59) I 1 r Q l ".5.GOVIINIIENI PR IN'III IG OFFICE: ID! 0-856-S3L

1. A method of making a spool valve structure having a cylindrical coremember rotatably enclosed in a sleeve member, said method comprising thestep of forming in a single machine operation a first perforationentirely through both of said members on a transverse axis parallel toand offset to one side of a plane containing the longitudinal axes ofsaid
 2. The method according to claim 1 wherein said members areretained against movement relative to each other during said formingoperation.
 3. The method according to claim 2 and including the step oFforming a second perforation as therein defined, said two perforationsbeing spaced radially from each other.
 4. The method according to claim2 and including the step of forming a second perforation as thereindefined, said two perforations being spaced longitudinally from eachother.
 5. The method according to claim 3 and including forming saidfirst and second perforation on axes offset from opposite sides of saidplane.
 6. The method according to claim 4 and including forming saidfirst and second perforation on axes offset from opposite sides of saidplane.
 7. The method according to claim 4 and including the step offorming an axially extending hole in said core member to effect fluidconnection between said first and second perforations.
 8. The methodaccording to claim 2 wherein said perforation is in the form of aperipheral channel with congruent boundaries at the interface of saidcore and sleeve members.
 9. The method according to claim 8 wherein asecond peripheral channel is formed in said core.
 10. The methodaccording to claim 2 wherein said perforation is a generally cylindricalhole with congruent boundaries at the interface of said core and sleevemembers.
 11. The method according to claim 4 wherein said firstperforation is a peripheral channel and said second perforation is acylindrical hole.
 12. The method according to claim 4 wherein both saidperforations are peripheral channels.
 13. The method according to claim1 and including forming a second perforation in said sleeve memberintermediate said two ports.
 14. The method according to claim 2 inwhich said forming operation is electrical discharge machining.
 15. Themethod according to claim 2 wherein the step of retaining said core andsleeve members against movement comprises applying an adhesive materialto said members prior to said forming operation and removing saidadhesive material subsequent to said forming operation.
 16. The methodaccording to claim 14 and including using a meltable epoxy material toretain said sleeve and core member against movement.
 17. The methodaccording to claim 15 and including the steps of using electricaldischarge machining and then melting said epoxy material to permit saidcore and sleeve members to be separated from each other following theperforation forming step.